Clone session with thinking blocks stripped

[gadflysu]

Problem

When switching from a third-party LLM endpoint (e.g. mimo) to AWS Bedrock mid-session, Claude Code carries over conversation history containing `thinking` blocks with an empty `signature` field. Bedrock strictly validates `signature`, so any subsequent request fails with:

```
API Error: 400 messages.1.content.0: Invalid `signature` in `thinking` block
```

Goal

Clone an existing Claude session JSONL with all `thinking` blocks stripped, so the clone can be resumed under a strict endpoint. Source session is never modified.

Proposed UX

CLI:
```
aps clone --strip-thinking
```
Prints new session ID and cd "<cwd>" && claude --resume <new-id>.

Interactive: T on a selected session → confirm prompt → clone+strip → show new ID in status bar. Stay in picker, no auto-launch.

Clone Logic (based on CC /branch source)

1. Read source JSONL; skip isSidechain: true entries and non-transcript entries
2. Assign new UUID as sessionId; rebuild parentUuid chain
3. Keep all other fields intact (uuid, timestamps, cwd, gitBranch, etc.)
4. Add forkedFrom: {sessionId, messageUuid} for traceability
5. With --strip-thinking: filter out {"type":"thinking",...} blocks from every assistant content array
6. Copy content-replacement entries (rewrite their sessionId to the new UUID)
7. Write to same project dir as <new-uuid>.jsonl

Plan

docs/agent/plan-issue-47-clone-strip-thinking.md

Acceptance Criteria

• Source session never modified
• New session ID + resume command printed to stdout
• Works from CLI subcommand and interactive picker keybinding (T)
• Session ID argument supports full UUID and unambiguous prefix